1. Field
The embodiments described herein relate generally to linear accelerator system. More particularly, the described embodiments relate to geometric calibration of linear accelerator system elements.
2. Description
A linear accelerator produces electrons or photons having particular energies. In one common application, a linear accelerator generates a radiation beam and directs the beam toward a target area of a patient. The beam is intended to destroy cells within the target area by causing ionizations within the cells or other radiation-induced cell damage.
Radiation treatment plans are intended to maximize radiation delivered to a target while minimizing radiation delivered to healthy tissue. To design a radiation treatment plan, a designer must assume that relevant portions of a patient will be in particular positions relative to a linear accelerator during delivery of the treatment radiation. The goals of maximizing target radiation and minimizing healthy tissue radiation may not be achieved if the relevant portions are not positioned in accordance with the treatment plan during delivery of the radiation. More specifically, errors in positioning the patient can cause the delivery of low radiation doses to tumors and high radiation doses to sensitive healthy tissue. The potential for misdelivery increases with increased positioning errors.
Conventional imaging systems may be used to verify patient positioning prior to the delivery of treatment radiation. For example, a low-dose radiation beam is emitted by a linear accelerator prior to treatment, passes through a volume of the patient and is received by an imaging system. The imaging system generates a two-dimensional portal image of the patient volume, which can be used to determine whether the patient is in a position dictated by the particular treatment plan. This determination, however, presumes a particular geometric relationship between the imaging device and the treatment head. Accordingly, the accuracy of the determination depends on whether the imaging system is positioned in accordance with presumed geometric relationship.
Due at least in part to the foregoing, treatment plans are designed under the assumption that positioning errors may occur and may result in misdelivery of radiation. Treatment plans compensate for this potential misdelivery by specifying lower doses and/or using larger beam shapes than would be specified if misdelivery was not expected. Such compensation may decrease as margins of error in patient positioning decrease.
It would therefore be beneficial to provide a system and method that efficiently improves the determination of a patient position with respect to a radiation beam path. When used in conjunction with conventionally-designed treatments, such an improved determination may reduce chances of harming healthy tissue and may allow the use of more aggressive treatments. Specifically, if a margin of error in patient positioning is known to be small, treatment may be designed to safely radiate a greater portion of a tumor with higher doses than in scenarios where the margin of error is larger.